It is known that a relative measure of intracranial pressure may be non-invasively obtained by measuring changes in a patient's skull diameter with a sonomicrometer or similar volumetric measurement type device. According to the known method, changes in the patient's skull diameter are directly related to changes in the patient's intracranial pressure. Because, however, the measured changes in skull diameter are extraordinarily small, indications of intracranial pressure obtained through this method are highly subject to vibration and/or slow drift artifacts. While vibration artifacts, such as may result from touching of the patient, may generally be removed from the estimate through simple low pass filtering, this is not the case for slow drift artifacts, such as may result from patient movements and the like. Slow drift artifacts are generally indistinguishable in the frequency domain from changes in intracranial pressure caused by edema, infectious process, tumor growth or bleeding. As a result, slow drift artifacts are generally very difficult to remove through standard filtering techniques.
It is therefore a primary object of the present invention to improve over the prior art by providing a method whereby slow drift type artifacts may be eliminated from the sonomicrometer obtained signals, thereby improving the quality of intracranial pressure measurement data derived therefrom. Although those of ordinary skill in the art will recognize that one such means for accomplishing this objective involves securing the sonomicrometer to the patient's skull with bone screws or the like, such a solution completely destroys the sonomicrometer's non-invasive character. As a result, it is a further object of the present invention to meet the primary object without sacrifice of the overall technique's non-invasive character.